Ceramic components are used extensively throughout many industries and have been formed in a variety of complex shapes. Typically these complex shapes must be machined after the ceramic component is fully, or at least partially, fired and therefore in an extremely hard condition, since the unfired ceramic compact is typically too soft to withstand extensive machining. The machining of the partially or fully fired ceramic component is expensive and difficult because of the hard brittle nature of the ceramic material after firing, even after only partial firing.
Generally, a ceramic component is formed by first compacting an appropriate powder mixture so as to form a ceramic green compact which resembles the desired shape of the component, and then firing the green compact at the appropriate temperature to consolidate and vitrify the ceramic powders.
Typically, an organic binder is included within the ceramic powder mixture prior to forming the green compact, so as to help consolidate the powder mixture during compaction. The addition of a binder has been necessary to provide sufficient strength to the unfired green compact, so as to facilitate the subsequent handling and/or machining of the compact before firing of the compact. The types of binders which have been routinely employed include dry, flaky binders or liquified binders. These binders have been added to the ceramic powders before the powders are blended so as to ensure intimate commingling between the ceramic powder and the binder.
If a dry binder is employed within the ceramic powder mixture, various consolidation operations may be used, such as dry pressing, high energy compaction or vibratory packing. These dry pressing techniques have required the addition of a binder before powder compaction so as to promote die lubrication and powder deformability during pressing. In addition, the binder provides the pressed compact with some strength for subsequent handling, prior to densification of the compact during firing. However, despite the thorough mixing of the binder and powders, the particles do not always uniformly consolidate. Therefore the density of the unfired, green compacts formed from these dry binder operations may vary considerably. Further, even though the binder provides some enhancement of strength within the compact, the compact still can not tolerate any type of machining other than gentle surface polishing or light machining, which unduly limits the use of these ceramic components to relatively simple shapes.
Alternatively, a liquified binder may be mixed with the powder mixture. With a liquified binder, the ceramic powders may be consolidated by techniques such as injection molding, slip casting or filter-pressing. The binder has been necessary when using these wet compaction techniques, so as to promote sufficient deflocculation of the powders within the liquid mixture and/or to promote fluidity of the powders. In addition, the binder provides a degree of strength to the compact for subsequent handling and light machining prior to firing, however complex machining of the compact is precluded due to the insufficient strength of the compact.
Therefore, although the use of binders for enhanced compaction of the ceramic powder mixtures is well entrenched within the ceramic processing industry, it is apparent that these conventional manufacturing processes are less than ideal, particularly since the traditional unfired compacts can not withstand significant amounts of machining. Thus, it would be desirable to provide an unfired, ceramic compact which is sufficiently strong and rugged to withstand machining into complex shapes. Further, it would be desirable to provide a method for forming these types of machinable, unfired ceramic compacts, wherein the binder can be uniformly distributed in those regions of the compact where the presence of binder is desired, such as for enhanced machinability.